The present invention relates to a "digital" typesetter for imaging graphics quality characters of a specified font which is stored in the machine in digital form.
Digital typesetters image typographical characters which have been coded in digital form and stored on some kind of digital storage medium such as a magnetic tape, drum or rigid or floppy disk. Such digital typesetters are normally provided with a cathode ray tube (CRT) or laser beam imaging system for writing characters onto photographic film or paper. In the case of digital CRT typesetters, successive characters are each completely imaged, one at a time, by the CRT beam which is position-controlled in two dimensions by the CRT X-Y deflection voltages. Normally, each character is built up from a series of vertical strokes which commence from the left side bearing of the character and proceed successively to the right side bearing. Once a character has been completely stroked, the CRT beam is moved to the left side bearing position of the next successive character, and so on.
When a laser beam rather than a CRT imaging system is used to image typographical characters on film or paper, a modulated one dimensional scan has generally been used. In this case, the character-writing beam is swept across the entire width of the output film or paper in a single line and this print medium is moved in a direction transverse to the direction of the scan line. While such a laser-based imaging system is substantially less expensive than a cathode ray tube system, such a system requires computation of the beam switch points to turn the scanning beam on and off with sufficient speed to keep up with the scanner on a real time basis. In order to overcome this problem, the characters of each font have been digitized as a separate digital master for each type-size to be set. In this way, the encoded character information may be used directly without scaling, for example, which requires extensive computation. The disadvantage of this arrangement is that an entire font of characters must be stored in the machine for each of the desired type sizes. This results in excessive use of storage space within the machine or requires that the machine be repeatedly "dressed" with a different digitally-encoded font each time a different type size, or a different font are to be used.